The present invention relates to an objective lens switching device in an optical apparatus such as a microscope, in which device an objective lens with a desired magnification suitable for a viewed object is selected from among a plurality of objective lenses and positioned on a viewing optical path.
An objective lens switching device, generally called a revolver, has been used in an optical apparatus such as a conventional microscope and in the device, an objective lens with a desired magnification has been selected so as to be suitable for a viewed object and positioned on a viewing optical path. In such an objective lens switching device, a revolver moving section is revolved by driving a motor with a predetermined voltage and revolution of a revolver is stopped with provision of a mechanically engaging mechanism between the revolver moving and stationary sections. The engaging mechanism works such that each time when an optical axis of each objective lens mounted on the revolver coincides with a viewing optical axis of the optical apparatus such as a microscope, the revolver moving and stationary sections are mechanically engaged and thus the objective lens is positioned for holding in place.
Such structures have been disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 5-281457 and 7-311343, and Published Japanese Patent No. 2539903.
FIG. 1 is a sectional view showing an example of a structure of a conventional revolver switching device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-281457 (hereinafter referred to as first conventional example).
As shown in FIG. 1, this switching device comprises: a revolver 4 on which a plurality of objective lenses 2 are mounted; a motor 6 which revolves and brakes the revolver 4; and a transfer mechanism 8 which transfers rotation of the motor 6 to the revolver 4. Besides, this switching device comprises a mark plate 10 having two index sections which give a deceleration timing and a stop timing of the motor 6 to a rotary shaft of the motor 6 or the transfer mechanism 8.
On the other hand, the stationary section of the switching device is provided with a first and second sensors 12, 14 are provided respectively corresponding to the two indexes, With these indexes in use, deceleration of the motor 6 gets started when a desired objective lens 2 reaches before the optical axis, the motor 6 is stopped when the desired objective lens 2 reaches a point in the vicinity of the optical axis after deceleration of the motor 6 is sufficiently decelerated and thereby the desired objective lens 2 can quickly be positioned in place to align with the optical axis of the optical apparatus to precision.
Besides, the revolver 4 is provided with an engaging mechanism comprising a click ball 16 fixed to a rotary section and a leaf spring 18 fixed to a stationary section. A reference numeral 20 indicates a viewed object.
FIGS. 2 and 3 are views showing a structure a revolver device described Jpn. Pat. Appln. KOKAI Publication No. 7-311343 (hereinafter referred to as second conventional example).
In FIGS. 2 and 3, this revolver device comprises a microscope body 22 and an electric revolver body 24. In more detail, the revolver device comprises: a revolver 26 holding a plurality of objective lenses, not shown; a motor 28 for revolution and braking of the revolver 26; a positioning section 30 for mechanically stopping the revolver 26 at a predetermined position which has been decelerated by braking with the motor 28; a revolver control circuit 46 in a control section 42 for controlling the motor 28; and a fixed-amount revolution detecting section 32 for detecting revolution of the revolver 26 by a predetermined amount.
The fixed-amount revolution detecting section 32 is provided with a light interceptor 36 having a photo-interrupter 34 and notches 36a. The revolver 26 is provided with a rail 40 with which a spherical member is in a sliding contact.
The microscope body 22 is provided with an operating section 40 issuing a command of revolving the revolver 26 and a revolver control circuit 46 including a braking command circuit 48 and a motor output circuit 50.
The revolver device is constituted such that the control circuit 46 receives a detection result from the fixed-amount revolution detecting section 32 through a delay circuit 44 and braking of the motor 28 gets started after a preset time length of a delay is elapsed.
With such a constitution in use, since adjustment for correct positioning of a desired objective lens is enabled by electrical adjustment of a delay time length, an adjustment operation can be saved in terms of labor.
FIG. 4 is an illustration of a structure of a revolver revolving device (hereinafter referred to as a third conventional example) disclosed in Published Japanese Patent No. 2539903.
This revolver rotating device comprises: a motor drive apparatus 54 for revolving a revolver 52; a code apparatus 56 detecting a position of revolution of the revolver 52; a key board 58 and a remote control connecting terminal 60 as a selecting means for selecting in advance a revolver hole which is a target position; a control section 62 for controlling the number of rotation of the motor drive apparatus 54; and an engaging means, not shown, for fixing the selected revolver hole at the target position.
Deceleration marks 66 for the start of braking of the revolver 52 in correspondence to the number of the objective lenses are disposed on a code disc 64 of the code apparatus 56 and the number of rotation of the motor drive apparatus 54 is decreased before the revolver 52 reaches the target position with the help of cooperation of the marks 66 and the sensor 68. Hence, a desired objective lens can quickly be positioned at a target potion to precision. A reference numeral 70 indicates a taco generator and 72 a circuitry network.
However, a request for automation of a revolver switching device in recent years has been harder to be met in the aforementioned examples. That is, while there have been requests of increasing the number of objective lenses mounted and shortening a switching time between objective lenses, these are incompatible requests. In order to enable theses incompatible requests to be compatible, there is a need for controlling revolution of the revolver so that the revolver achieves correct and quick positioning of a desired objective lens on an optical axis.
However, since mounting conditions of objective lenses (the number of the objective lenses, kinds thereof and mounting positions thereof) are varied for different users and thereby a load imposed on a motor in revolving a revolver is also changed. Hence the most suitable control to stoppage has been difficult to be realized.
For example, in the first conventional example, when a desired objective lens 2 is positioned on an optical axis, a reflection type sensor 12 detects a reflection pattern of the mark plate 10 before the click ball 16 enters an engaging range of the leaf spring 18 and an electronic control circuit sufficiently decelerates rotation of the motor 6 with this detection signal on hand. Then, when the click ball 16 enters the engaging range of the leaf spring 18, the transmission type sensor 14 detects a notch in the mark plate 10. The electronic control circuit completely stops rotation of the motor 6 in response to the detection signal and thereby the click ball 16 enters the engaging range of the leaf spring 18 in an engaged manner and the desired objective lens 2 comes to be held on the optical axis.
Positional relations between the reflection type sensor 12 and the refection pattern of the mark plate 10, and between the transmission type sensor 14 and the notch of the mark plate 10 are optimized by correct adjustment in assembly so that engagement between the click ball 16 and the leaf spring 18 can be secured.
However, in the case of the first conventional example, the mark plate 10 having two index sections which give a deceleration timing and a stop timing of the motor 6 is not mounted on a rotary shaft of a turret, but on a rotary shaft of the motor 6 or the transfer mechanism 8. For this reason, when a backlash of the transfer mechanism 8 is large or there is a spatial fluctuation in each of objective lens switching devices, adjustment in positional relations between each sensor 12, 14 and the mark plate 10 is difficult. Besides, since there are inevitable adjustments both of the reflection type sensor 12 and the transmission type sensor 14 with correctness, it takes a long time to perform the adjustments.
In addition, while a load inertia to the motor 6 is greatly different according to a different mounting condition of objective lenses (the number of the objective lenses, kinds thereof, mounting positions thereof and the like), adjustment in a positional relation is always fixed regardless of the mounting condition. In any case, very difficult is adjustment of positions of the sensors 12, 14 and the mark plate 10 in a manner such that engagement between the click ball 16 and the leaf spring 18 is secured with neither overrun nor shortage of revolver 4.
Furthermore, in the second conventional example shown in FIGS. 2 and 3, adjustment of timing in braking of the motor 28 in order to position a desired objective lens on the optical axis is performed by electric means.
After the revolver 26 is activated, for example the photo-interrupter 34 detects the notch 36a of the light intercepting plate 36 and outputs the detection output, wherein for example, the photo-interrupter 34 and the light intercepting plate 36 are provided as the detecting section 32 for detecting that revolution is made by a fixed amount. The control circuit 46 receives the detection output and outputs a delay output after a preset time length of a delay is elapsed and with this timing, braking of the motor 28 is carried out. If a delay time length is changed, adjustment of timing in braking can be adjusted with no adjustment of a position of the light intercepting plate 36. The delay time length is optimally adjusted in each revolver device so that the click ball 38 is run over or stopped before a V groove 40.
However, since the delay time length is a fixed value for each revolver device and therefore cannot correspond to a change in a mounting condition of an objective lens (the number of the objective lenses, kinds thereof and mounting positions thereof), there is a risk that the click ball 38 cannot properly engage in the groove 40 in a mounting condition. On the other hand, if a change over time in use of the revolver device causes a change in a load on the motor 28 or motor characteristics themselves, such an inconvenience described above is further apt to occur.
Besides, in the third conventional example shown in FIG. 4, deceleration marks 66 corresponding to the number of objective lenses which marks are provided in order to start braking of the revolver 52 are formed on a code disc 64 each in the optimal size such that a desired objective lens may quickly be located at a target position with correctness.
However, in the third conventional example as well, a braking effect of a revolver 52 caused by a deceleration mark 66 is fixed in each revolver device and there 4 is a problem, therefore, the braking effect cannot sufficiently be adapted for the above mentioned mounting condition of an objective lens or a change over time in use.
As a common problem in the above mentioned first to third examples, there can be raised an inconvenience that a braking condition of a motor cannot be changed so as to be suitable for a kind of objective lens for substitution. That is, in any case, a switching speed (time required for switching) is changed by a change in the mounting condition of an objective lens or the like.
In addition, if a speed is changed, a shock when a sudden stoppage occurs is naturally changed with a variety in degree in each condition. The shock in the stoppage not only influences durability (abrasion resistance) but also scatters dust and dirt around the device, which thereby causes a great problem if a switching device is necessary to be used in a specifically clean environment (for example, clean room and the like).
Especially when a liquid immersion objective lens such as an oil immersion objective lens, a water immersion objective lens or the like is positioned on a viewing optical axis of an optical apparatus such as a microscope, there arises a problem of bubble production. When switching between objective lenses is performed in a manual operation, it is only required to conduct a switching action slowly and deliberately so as not to produce bubbles with all possible efforts. However, in the case of a conventional switching device which is electrically operated, since the same braking action has been applied regardless of a kind of objective lens for substitution, there has been arisen inconvenience that a leading edge of an objective lens comes to contact a specimen surface at a great speed on which water or oil adheres and as a result bubbles are inevitably produced.